I have read on another forum that the $1 per gallon sale is starting 8/28 at Petco. Dont know if this date is accurate but it should be coming soon. Employees at Petco have also told me it should be in early September. They have also said (as did the source at the other forum) that the tank sale includes aquariums up to 75 gallons. Past sales have only advertised tanks to 55 gallons.
Rumors galore - so stay on the look out.